1. Field of the Invention
This invention relates to an image forming apparatus, and particularly to an image forming apparatus in which the surface of an image bearing member is adapted to be cleaned by a cleaning blade.
2. Related Background Art
In some image forming apparatuses according to the prior art, a toner residual on the surface of an image bearing member after a toner image formed on the surface of the image bearing member has been transferred to a transferring material is adapted to be removed by a cleaning blade. FIG. 5 of the accompanying drawings schematically shows the construction of the image forming portion of such an image forming apparatus according to the prior art, and in FIG. 5, the reference numeral 1 designates an image bearing member. This image bearing member 1 is adapted to be rotatively driven in the direction of arrow a by driving means, not shown.
Also, around this image bearing member 1, there are disposed a primary contact electrifying roller 2 which is electrifying means (electrifying member) for electrifying the surface of the image bearing member 1 to uniform potential, a developing apparatus 5 which is developing means for causing a toner to adhere to an electrostatic latent image formed on the surface of the image bearing member 1 and forming a toner image thereon, a cleaning apparatus 8 for removing any toner residual on the surface of the image bearing member 1, etc.
In FIG. 5, the reference numeral 11 denotes a process cartridge compactly containing the image bearing member 1, the primary contact electrifying roller 2, the developing apparatus 5, the cleaning apparatus 8, etc. in a housing 9 and making them into a cartridge, and this process cartridge 11 is detachably mounted with resect to the image forming apparatus. Also, the reference numeral 10 designates a transfer electrifying roller which is a transferring member for transferring the toner image on the surface of the image bearing member onto a transferring material P, and this transfer electrifying roller 10 is adapted to contact with the image bearing member 1 when the process cartridge 11 is mounted.
In the thus constructed image forming apparatus, exposure light L from exposing means, not shown, is applied to the image bearing member 1 having had its surface electrified by the primary contact electrifying roller 2 to thereby form an electrostatic latent image on the surface of the image bearing member 1, whereafter this electrostatic latent image is developed by the developing apparatus 5 to thereby form a toner image on the image bearing member.
Thereafter, the toner image is transferred onto the transferring material P passing through the nip between the transfer electrifying roller 10 and the image bearing member 1, by the transfer electrifying roller 10. The transferring material P onto which the toner image has thus been transferred is thereafter conveyed to a fixing apparatus, not shown, and is heated and pressurized in this fixing apparatus, whereby the toner image is fixed.
Now, the developing apparatus 5, as shown in FIG. 5, is provided with a developing sleeve 3 rotated in the direction of arrow b for carrying the toner, not shown, and an elastic blade 4 for regulating the thickness of a toner coat on the developing sleeve 3. Also, the cleaning apparatus 8 is provided with a cleaning blade 6 (hereinafter referred to as the blade) supported by a supporting member 13 to scrape off any untransferred toner from the image bearing member 1, a dip sheet 7 for collecting the scraped-off untransferred toner, and a cleaner container 8a for containing the scraped-off toner therein.
Further, as shown in FIG. 6 of the accompanying drawings, cleaning end portion seals 14 which are seal members formed of an elastic material such as foamed polyurethane are provided on the opposite end portions of the blade 6 on the cleaner container with the gaps thereof with respect to the blade 6 made infinitely small so as not to leak the scraped-off toner from the cleaner container 8a. That is, the area which can collect the toner in the cleaning apparatus 8 is an opening portion (toner collecting opening) surrounded by the blade 6, the dip sheet 7 and the blade end portion seals 14 which is indicated by a halftone portion.
As the blade 6 of this cleaning apparatus 8, urethane rubber is often used usually from the viewpoint of durability, but urethane rubber is high in degree of adhesion and bad in slidability and therefore, a lubricant such as silicon resin fine particles or fluorine particles is applied to the edge portion of the blade (the fore end portion of the blade) which is the portion of contact with the image bearing member 1 to thereby obtain lubricity.
Now, in the prior-art image forming apparatus provided with such a blade 6, the lubricant may come off the blade 6 in some cases, and when the lubricant thus comes off, the friction between the blade 6 and the image bearing member 1 becomes great.
When the friction becomes great as described above, the blade 6 comes to receive a force in the direction of arrow F indicated in FIG. 5 because it abuts against the surface of the image bearing member 1 in a counter direction, whereby the blade edge is reversed in the direction of arrow F and turn-up of the blade 6 occurs. That is, the blade 6 obtaining lubricity by having a lubricant applied thereto will instantly cause turn-up thereof particularly under high temperature and high humidity if the lubricant comes off.
Description will now be made of the cause for the coming-off of this lubricant.
If the material of the blade 6 is urethane rubber, when the electrification polarity of the blade 6 frictionally sliding with respect to the image bearing member 1 is measured, the blade 6 is electrified to the plus polarity. On the other hand, silicon resin fine particles or fluorine particles which are the lubricant are electrification-serially minus, but the lubricant present in the form of fine particles is often minus by triboelectrification as a matter of course, and because of triboelectrification, there are also present fine particles electrified to plus. Consequently, the plus-electrified blade 6 retains the minus-electrified lubricant thereon, but conversely electrically repels the plus-electrified fine particles, whereby the lubricant tries to come off the blade 6.
On the other hand, for example, in a reversal developing system, when a toner electrified to minus is used, the primary contact electrifying roller 2 effects minus electrification and the transfer electrifying roller 10 effects plus electrification.
That is, in the reversal developing system, the toner is used for development in a portion lowered in electrification potential by being exposed and therefore, design is made such that in the opposite end portions which are not desired to be toner-developed, the primary electrification area width is secured widely and minus electrification is effected so that the toner may not be used for development. Accordingly, as shown in FIG. 7 of the accompanying drawings, the primary contact electrifying roller 2 is greater in length than the transfer electrifying roller 10.
Here, paying attention to the electrification potential of the surface of the image bearing member, the hatched portions of the surface of the usually minus-electrified image bearing member (organic photosensitive drum) which are shown in FIG. 7 are always minus-electrified by the primary contact electrifying roller 2. In contrast, the surface potential does not become uniform in that range of the surface of the image bearing member which is electrified by the transfer electrifying roller 10, but is electrified substantially plus after that range has passed the transfer electrifying roller 10.
In the lengthwise range which is thus electrified by the transfer electrifying roller 10, the surface of the image bearing member is plus-electrified, but the minus-electrified lubricant both electrically and physically firmly adheres to the plus-electrified blade 6 and does not come off.
However, in the primary electrification areas at the opposite ends of the transfer electrifying roller 10 which the electrification by the transfer electrifying roller 10 does not reach, the lubricant comes off because the surface potential of the image bearing member 1 is minus potential and in addition, the plus-electrified lubricant is repelled from the blade 6 electrified to electrically plus.
This lubricant having come off adheres to the primary contact electrifying roller 2 and contaminates the primary contact electrifying roller 2. The lubricant which has not adhered to the primary contact electrifying roller 2 again returns to the cleaning apparatus 8 if it does not adhere to the transferring material P, but in most cases, it is scraped off by the blade 6 and is collected into the cleaner container 8a and therefore is not useful as the lubricant.
The cause for turn-up of the blade will now be described with reference to FIGS. 8 and 9 of the accompanying drawings. FIG. 8 is a cross-sectional view of the transfer electrification area of the image bearing member 1, and FIG. 9 is a cross-sectional view of the primary electrification area outside the transfer electrification area of the image bearing member 1. Also, in these figures, ◯ indicative of the polarities indicates the lubricant, and the other polarities are indicative of the surface potential of the image bearing member 1 and the electrification potential of the blade 6.
Here, the opposite end portions of the primary contact electrifying roller 2 are brought into pressure contact with the surface of the image bearing member by springs, not shown, whereby the primary contact electrifying roller 2 is driven to rotate with the rotation of the image bearing member 1. In this case, the pressure force of the springs is high in the opposite end portions of the primary contact electrifying roller 2 as compared with the central portion thereof and therefore, in the opposite end portions, the surface material of the primary contact electrifying roller 2, though slightly, is rubbed against and shifts to the surface of the image bearing member.
By the surface material of the primary contact electrifying roller 2 thus shifting to the surface of the image bearing member, the friction between the blade 6 and the surface of the image bearing member 1 becomes great and thus, the blade 6 is turned up.
Also, in the area of contact of the primary contact electrifying roller 2 with the image bearing member 1, discharge occurs to uniformly electrify the surface of the image bearing member 1. That is, a discharge product is created in the electrification area and this discharge product adheres to the surface of the image bearing member 1, whereby the lubricity of the surface of the image bearing member 1 is reduced.
In that area of the primary contact electrifying roller 2 which is the area of contact, but in which the transfer electrifying roller 10 is in contact with the surface of the image bearing member 1, the toner image, the transferring material or the transfer electrifying roller 10 itself is cleaning the surface of the image bearing member 1 and therefore, as compared with the area in which the primary contact electrifying roller 2 alone contacts, in the area wherein the transfer electrifying roller 10 is in contact with the surface of the image bearing member 1, the surface of the image bearing member 1 does not become difficult to slide.
On the other hand, in many cases, an alternating current electric field is superimposed on the primary contact electrifying roller 2 to uniformize the electrification potential, and when the alternating current electric field is superimposed like this, the image bearing member 1 and the primary contact electrifying roller 2 come to repeat attracting each other and separating from each other under the influence of the alternating current electric field, and the image bearing member 1 and the blade 6 also come to manifest similar behavior therebetween.
As a result, the fore end of the blade flaps to thereby clear the lubricant away, and when the image bearing member 1 is moved away from the blade 6, the fore end of the blade becomes erect and when in this state, drive is applied, turn-up of the blade comes to be induced and further, turn-up of the blade 6 becomes severe.
As described above, when the primary contact electrifying roller 2 and the transfer electrifying roller 10 are used, the applied agent electrically comes off the blade 6 in the electrification area of the primary contact electrifying roller 2 and outside the electrification area of the transfer electrifying roller 10, and the frictional force becomes excessively great from the portion of the blade from which the applied agent has come off and the primary contact electrifying roller 2 makes the surface of the image bearing member difficult to slide, whereby turn-up of the blade 6 is caused.
In order to solve this problem, there is an apparatus in which as shown, for example, in Japanese Patent Post-Exam Publn No. 6-44180 and Japanese Patent Post-Exam Publn No. 6-58585, lubricant supplying means is provided near the opposite end portions of a cleaning blade to which a toner is not supplied.
However, as already described, the portion from which the lubricant comes off is an area not supplied with the toner which is outside the developing area, but occurs outside the transferring area which is outside it. Accordingly, in such a case, the lubricant can be supplied to the outside of the transferring area, and the supply of the lubricant to the inside of it and the outside of the developing area is useless. If the lubricant is supplied from the edge of the developing area to the end portions of the blade 6, this lubricant may enter the image area and disturb the image.
Also, in Japanese Patent Application Laid-Open No. 8-123279, there is described an apparatus in which a lubricant is infiltrated into cleaning end portion seals on the opposite end portions of a blade to thereby supply the lubricant to the end portions of the blade. However, the apparatus of such a construction in which the lubricant is supplied from the cleaning end portion seals cannot supply the lubricant in the course of the operation and therefore suffers from a difficultly in respect to continuity.
Also, if the amount of lubricant is made great from the initial state, when excessive supply is done at a time, the lubricant scraped off by the blade 6 may leak out of the cleaner and fall onto the transferring material conveyed, because the cleaning end portion seal areas are not areas capable of collecting as the cleaner.
When the lubricant thus falls onto the transferring material, it will disturb the image, and when the lubricant falls into the image forming apparatus, it will stain the interior of the apparatus and again it will come to adhere to the transferring material.
It is an object of the present invention to provide an image forming apparatus in which good cleaning can be effected stably.
It is another object of the present invention to provide an image forming apparatus in which turn-up of a cleaning blade is prevented.
It is still another object of the present invention to provide an image forming apparatus in which a lubricant can be stably supplied to the end portions of a cleaning blade.
Further objects and features of the present invention will become more apparent from the following detailed description when read with reference to the accompanying drawings.